ISIS Carries Out First ‘Serious’ Attack in Northern Iraq in Months, U.S. Says

ERBIL, Iraq — Islamic State fighters conducted their most significant military operation in northern Iraq in more than five months when they mounted a three-pronged attack on Wednesday night north and east of Mosul, American officials said Thursday.

The attack appeared to have been intended to show that the group is still a potent fighting force despite setbacks in Sinjar, Iraq, and in northern Syria. It may have also been intended to disrupt efforts by the American-led coalition to prepare for the eventual battle to retake Mosul, Iraq’s second-largest city, which was captured by the Islamic State in June 2014.

The assault, which took place on the eve of a visit here by Defense Secretary Ashton B. Carter on Thursday, was beaten back by American and allied airstrikes and fierce fighting by pesh merga fighters, as the Kurdish forces are known. Dozens of the Kurdish fighters were killed, according to Kurdish officials.

“I think their principal objective was probably to conduct a spoiling attack,” said Brig. Gen. Mark Odom, the senior American officer in northern Iraq, referring to the possibility that the attack may have been intended to disrupt moves to encircle and eventually capture Mosul.

“As attacks go, they were pretty significant,” General Odom added. “The last time we had a serious attack was on 6 July.”

The coordinated attacks took place at Narwan, Bashiqa and Tal Aswad. Each of the assaults, General Odom said, involved 80 to 120 Islamic State fighters who maneuvered in small formations and used armored bulldozers, trucks with mounted machine guns and vehicles driven by suicide bombers.

American officials estimated that 180 Islamic State fighters were killed in the airstrikes, which were carried out by American, British and French aircraft. The bombing lasted until 9 a.m. Thursday. American officials believe pesh merga fighters killed hundreds more of the militants, though precise figures were not available.

The larger questions, however, are what the attack said about the militants’ capacities and how the Obama administration might pursue its goal to roll back the group’s self-declared caliphate.

Citing the attack, Kurdish officials renewed their longstanding appeal for more armored vehicles, more ammunition and specialized equipment like night-vision gear, which they insist they need to contend with the Islamic State, also known as ISIS or ISIL.

“The last 24 hours are a grim reminder of why we should not underestimate ISIS and how badly the pesh merga need more ground support in addition to continued air support,” said Masrour Barzani, the chairman of the Kurdish region’s security council.

After his meeting with Massoud Barzani, the president of the Kurdish autonomous region, Mr. Carter signaled that the Obama administration would accelerate some arms deliveries to the Kurds, though that falls short of what Kurdish officials would like.

The United States had promised to provide the weapons and equipment for two new combat brigades if the Kurds followed through with plans to establish units that would integrate fighters from the Kurds’ two main political parties: the Kurdistan Democratic Party and the Patriotic Union of Kurdistan.

But the Kurds have contended that forming the new brigades would be costly and time-consuming. So Mr. Carter said the Obama administration now planned to move ahead anyway with the delivery of the equipment, which is stored in Kuwait. The expectation, Mr. Carter made clear, is that the equipment will be used by the Kurds for the “encirclement of Mosul” after Iraqi forces retake Ramadi from the Islamic State.

During his visit here, Mr. Carter also met with several Special Forces commandos who were among the 50 who recently traveled to northern Syria to work with Syrian fighters and Kurdish forces there. A senior Defense Department official, who asked not to be identified in order to discuss a closed-door meeting, said that Mr. Carter was encouraged by their assessment of the effort to build a Syrian Arab force that could put pressure on Raqqa, the de facto capital of the Islamic State’s territory.

The landscape in northern Iraq is a complicated one. One coalition official, who spoke on the condition of anonymity to discuss intelligence reports, said that in recent weeks Turkey had sent about 1,000 troops, and a small number of tanks, to reinforce about 200 Turkish soldiers who have been involved in training local fighters.

The presence of the Turkish forces has been a major source of friction between Iraq and Turkey, and they were caught up in the recent fighting.

According to one coalition official, the Islamic State fighters who mounted the attacks on Wednesday managed to sneak into the Kurdish area and fired mortar shells at the Zilikan base in the Bashiqa area in northern Iraq where the Turkish troops are based.

But a spokesman for the Patriotic Union of Kurdistan in the region said that the Islamic State fighters were actually trying to target pesh merga forces in the area when they hit the Zilikan base by mistake.

Either way, four Turkish trainers were wounded, according to Turkish news reports.

Kamil Kakol contributed reporting from Sulaimaniya, Iraq.

A version of this article appears in print on , on Page A16 of the New York edition with the headline: ISIS Carries Out First ‘Serious’ Attack in Northern Iraq in Months, U.S. Says . Order Reprints | Today’s Paper | Subscribe